Field of the Invention
The invention relates to methods of creating composite materials with tailored spectral properties in the visible and invisible electromagnetic (EM) wave spectrum using a plurality of discrete populations of nano- and/or micro particles and/or nano- and/or micro cavities.
In some embodiments the invention relates to structural elements, which enable the design and construction of buildings or other confined spaces with improved thermal and energetic properties. In particular, the invention enables the construction of buildings, which absorb less solar radiation per given surface area. This results in lower temperatures inside buildings or other confined spaces, increased time to reach higher temperatures inside such buildings or predominantly confined spaces, and/or in reduced power requirements for air-conditioning systems.
Description of the Related Art
Many technical applications require to control the temperature inside predominantly enclosed spaces or, as a related aspect, the control the electromagnetic spectral properties of materials and surfaces. In some instances it may be desirable to keep the temperature inside predominantly enclosed spaces low, or even as low as possible, whereas in other applications the opposite may be the case. In yet other instances, for example related to achieving broadband camouflage effects, the electromagnetic spectral “appearance” may be of primary interest.
The broadband electromagnetic spectral properties of surface materials (within a certain wavelength range) can affect:                (a) how a material/surface visually appears,        (b) how readily visible and invisible electromagnetic radiation is absorbed from a surface and thus gets converted into thermal energy, and        (c) how rapidly a surface can lose thermal energy by emitting electromagnetic waves at thermal wavelength.        
The invention relates in particular to the design and manufacturing of composite materials, which have tailored and improved Ultraviolet (UV), visible (VIS), Near Infrared (NIR), Mid Infrared (MIR), and Far Infrared (FIR) properties, by containing tailored mixtures of nano- and micro particles. Henceforth the term ‘light’ shall be understood to apply for all of these spectral ranges, not only the portion visible to humans.
Embodiments herein may be described within the context of a range of electromagnetic frequencies ranging from UV to FIR, since these are of increased importance for visual appearance, thermal management, and camouflage. However, the invention should not be limited to these frequencies, as similar arguments can be made for other electromagnetic frequencies.
Thermal management of predominantly enclosed spaces, including buildings, can be a problem in geographic locations with relatively high levels of solar radiation, specifically in conjunction with high energy cost, which makes in some countries the use of permanent air-conditioning financially problematic for a significant segment of the population.
A considerable portion of the energy, which contributes to indoor temperatures, is the result of absorbed solar radiation by the building envelope. This effect can be true in tropical and subtropical regions, but it also applies in moderate climate zones, for example, during summer or times of increased relative temperature (e.g., in North America, Central and Southern Europe).
Related problems apply also to predominantly open spaces, such as large cities and densely populated areas in tropical and subtropical regions, where concrete and asphalt surfaces can significantly contribute to the common “heat island” effect in such areas.
Thus, reducing the amount of solar radiation, which is absorbed by the surface elements of predominantly enclosed spaces, including buildings, can contribute to reducing indoor temperature and/or reduce the required power for air-conditioning. Furthermore, widespread application of such advanced passive cooling methods can contribute to mitigate the heat island phenomena observed in large cities.
In some embodiments the disclosed invention can serve to fabricate materials and surfaces, which enable to control to a very high degree independently the spectral behavior in the VIS range and NIR range, i.e., optical color and NIR “color”.
In other embodiments of the disclosed invention, such as inside solar-thermal collectors, the exact opposite is the case: Here the target is to maximize the wavelength range and efficiency of conversions of solar radiation into thermal energy.
In yet other embodiments the disclosed invention, a goal is to achieve a close spectral match of surfaces against a given background, i.e. to “blend in” with the environment, preferable over a wide spectral range. Such effects are desirable in defense-related applications, for example surfaces of buildings (bunkers) or combat vehicles, to avoid, delay, or complicate optical, NIR, IR, or FIR (i.e., thermal) detection, including by ground-, air-, or space-based long-range multi-spectral imaging systems.